Continuous inkjet printer, printhead, and method of manufacturing electrodes

ABSTRACT

E1 A CIJ printhead includes a droplet deflector electrode having one or more windows formed therein, and a phase or velocity detector electrode disposed within the window. A method of forming the electrodes by plating multiple conductive and dielectric layers is also disclosed.

FIELD OF INVENTION

The present invention relates to continuous inkjet (CIJ) printers and,more particularly, to CIJ printers of the multi-nozzle type.

BACKGROUND ON THE INVENTION

Multi-nozzle continuous inkjet printers have been developed in order toprovide high quality, high speed printing. A row of inkjet nozzles atvery close spacings are provided and individual streams of ink issuefrom each of the nozzles continuously in use, being broken up intoindividual droplets automatically. The individual droplets are chargedappropriately to cause them to be printed or else deflected into agutter. Printers of this type are described, for example, in U.S. Pat.Nos. 4,613,871 and 4,427,986. the printers described in thesespecifications are of the type generally known as binary continuousmulti-jet.

In order to control the printing process accurately, it is known todetect both the velocity of the droplets being emitted from the dropletgenerator nozzles and to determine the phase of droplet charging withrespect to droplet generation by means of electrodes which extendtransverse to the path of the droplets.

The phase detection and velocity detection electrodes, as they areknown, can be disposed between the charge electrodes and the deflectionelectrode or electrodes. However, it is important to ensure that, foraccuracy of phase and velocity detection, the phase and velocitydetector electrodes are themselves very accurately positioned withrespect to the charge electrode.

SUMMARY OF THE INVENTION

The present invention is aimed at ensuring accurate location of thephase detector and/or velocity detector electrodes in a continuousinkjet printer.

According to the present invention a multi-jet CIJ printer has adeflection electrode having a window formed therein, a phase detector orvelocity detector electrode being disposed within the window.

Preferably, when forming a pair of detectors within the envelope of thedeflection electrode, the phase detector and velocity detector electrodeare formed, by a deposition process in which a non-conductive dielectricplate, preferably formed of alumina, is pre-drilled with a pair of holesspaced apart on the surface of the plate and a conductive material, forexample, gold, silver or other suitable conductive metal or composite isplated through the holes. Thereafter, one side of the dielectric plateis plated with a conductive layer which is not connected with theplating through the holes, the interior of the holes being filledthrough with a dielectric material such as glass to create a liquidtight barrier, and a pair of dielectric layers, one corresponding toeach of the detectors, are laid down, each of the dielectric layerssurrounding a respective one of the holes through the plate. On top ofthese dielectric layers the detectors are plated, for example, usinggold, silver or other suitable conductive material, each of theconductive layers forming the detectors being connected to theconductive plating through the respective hole. Further dielectriclayers are laid over the detectors and then the face of the plate isplated with a conductive material, to provide the deflection electrode,with a pair of windows being left above each of the detector areasbefore the detector areas are partly exposed within the windows.

On the other face of the dielectric plate a pair of conductive connectorpads may be formed in communication with the plated conductive layersthrough the holes and a conductive screen layer is plated onto thedielectric substrate around, but not in contact, with the conductivepads. A dielectric covering layer is then printed over the conductivelayer with a pair of small windows being left at the location of each ofthe conductive pads, one window of each pair being positioned directlyover the conductive pad and the other spaced from it so as to lie overthe conductive screen layer. This enables connection of the inner coreto the respective detector and the shield layer of a coaxial conductorto the shield (deflection electrode), with the conductor lyingsubstantially parallel to the face of the plate.

Locating the phase detector and/or velocity detector electrode orelectrodes within the face of the deflection electrode not only achievesa compact design, but also, since the deflection electrode is locatedaccurately with respect to the charge electrodes, achieves correspondingaccuracy of location of the phase detector and/or velocity detectorelectrodes with respect to the charge electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

One example of a deflection electrode with phase detector and velocitydetector electrodes formed in the face thereof will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a side view of the print head of a multi-nozzle CIJ printer asdescribed in our EP-A-0780231; and,

FIGS. 2 to 8 illustrate various stages in the manufacture of theintegrated phase detector and velocity detector electrodes.

DETAILED DESCRIPTION OF THE INVENTION

The printhead shown in FIG. 1 is described in more detail in ourEP-A-0780231. Since not all the features shown in FIG. 1 are relevantfor a description of the present invention only the primary featureswill be referenced and described.

The printhead has an electronics sub-system 1 by means of which arecontrolled the piezoelectric oscillator 2 forming part of a dropletgenerator 3 which has a nozzle plate 4 from which, in use, issue pluralstreams 5 of ink. The closely spaced nozzles are arranged in a rownormal to the plane of the drawing. The streams of ink break up intoindividual droplets which pass respective charge electrodes 6 alsoarranged in a row in the same direction, where they are selectivelycharged and then passed between a pair of deflection electrodes 7, 7′which establish, in use, an electric field by means of which chargeddroplets are deflected from their straight-line path into a gutter 8.Formed in the face of the deflection electrode 7 are a phase detectorelectrode and velocity detector electrode (neither of which is shown inFIG. 1) which are used to detect the charge applied to droplets by thecharge electrode 6 and the speed of the droplets respectively.

FIGS. 2 to 8 illustrate the phase detector electrode and velocitydetector electrode and their manufacture in more detail.

The phase detector 9 and the velocity detector electrode 10 are formed,together with the deflection electrode 7, by a deposition process, inwhich, as a first step (see FIG. 2) a non-conductive rectangulardielectric plate 11, preferably formed of alumina and pre-drilled with apair of holes 12 spaced apart on the surface of the plate, has aconductive material 13, for example, gold, silver or other suitableconductive metal or composite, plated through the holes 12. Thereafter(also FIG. 2), one side of the dielectric plate 11 is screen printed orotherwise plated with a conductive layer 14 which provides a shield inuse, and which is not connected with the plating 13 through the holes.The interior of the holes is then filled through with a dielectricmaterial 15 such as glass to seal them against liquid.

Next (see FIG. 3), on top of the conductive layer 14, a pair ofdielectric layers 16, one corresponding to each of the detectors, arelaid down, each of the dielectric layers surrounding a respective one ofthe holes 12 through the plate 11. On top of these dielectric layers 16,the detectors 9, 10 are then screen printed or otherwise plated (seeFIG. 4), for example, using gold, silver or other suitable conductivematerial, each of the conductive layers forming the detectors 9,10 beingconnected to the conductive plating 13 through the respective hole 12.

Further dielectric layers 17 are then (see FIG. 5) laid down over thedetectors, and then (see FIG. 6) the major part of the face of the plateis plated with a conductive material 18, with a pair of “windows” 19,20being left above each of the detector areas 9,10 before the detectorareas are partly exposed within the “windows”.

On the other face of the dielectric plate 11 (see FIG. 7) a pair ofconductive connector pads 21,22 are formed in communication with theplated conductive layers 13 through the holes 12 and a furtherconductive screen layer 23 is plated onto the dielectric substratearound, but not in contact with, the conductive pads 21,22. A dielectriccovering layer 24 is then printed over the conductive layer 23 with apair of small windows 24,25 being left at the location of each of theconductive pads 21,22, one window 24 of each pair being positioneddirectly over the conductive pad 21,22 and the other pad spaced from itso as to lie over the conductive screen layer 23. This enablesconnection of the inner core and the shield layer respectively of acoaxial conductor (not shown) to be made to the conductive pad 21,22 andshield 23 respectively, with the conductor lying substantially parallelto the face of the plate. This provides a secure shielded connection toeach of the detectors 9,10 in a simple manner which does not occupysignificant space on the side of the deflector plate opposite thedetectors 7,9,10.

What is claimed is:
 1. A method of manufacturing a phase or velocitydetector electrode and a deflection electrode for a CIJ printhead,comprising the steps of: a) providing a non-conductive dielectricsubstrate; b) providing at least one hole through the substrate; c)plating a conductive material, through the at least one hole; d) platingone side of the dielectric substrate with a conductive layer in suchmanner as to avoid connection with the plating through the at least onehole; e) filling the interior of the at least one hole with a dielectricmaterial to create a liquid tight barrier; f) forming a dielectric layersurrounding the at least one hole; g) plating, on top of the dielectriclayer, a conductive material to form at least one detector, the at leastone detector being connected to the conductive plating through the atleast one hole; h) providing a further dielectric layer over the atleast one detector; i) plating a face of the substrate with a conductivematerial to provide a deflection electrode, leaving a window above theat least one detector; and j) partly exposing the at least one detectorwithin the window.
 2. A method according to claim 1, further comprisingthe steps of: k) forming at least one conductive connector pad onanother face of the dielectric substrate in communication with theplated conductive layer through the at least one hole; l) plating aconductive screen layer onto the dielectric substrate around, but not incontact with, the at least one conductive pad; m) forming a dielectriccovering layer over the conductive layer with a pair of windows beingleft at a location of the at least one conductive pad, one window of thepair being positioned directly over the at least one conductive pad andthe other being spaced from said at least one conductive pad so as tolie over the conductive screen layer.
 3. A method according to claim 2,further comprising the steps of: n) connecting an inner core of acoaxial conductor to the at least one conductive pad and hence to the atleast one detector, and o) connecting a shield layer of the coaxialconductor to the screen layer, with the coaxial conductor lyingsubstantially parallel to the substrate.
 4. A method according to claim3, wherein said at least one detector comprises a pair of detectors andsaid at least one hole comprises a pair of holes.
 5. The methodaccording to claim 2, wherein said at least one conductive pad comprisesa pair of conductive pads.
 6. A method according to claim 2, whereinsaid at least one detector comprises a pair of detectors and said atleast one hole comprises a pair of holes.
 7. A method according to claim1, wherein said at least one detector comprises a pair of detectors andsaid at least one hole comprises a pair of holes.
 8. A multi-jetcontinuous inkjet printhead comprising: a dielectric substrate, an inkdroplet deflector electrode connected to said dielectric substrate, saidink drop deflector electrode disposed within said second window andconnected to said droplet deflector electrode, and a phase detectorelectrode disposed within said first window and connected to saiddroplet deflector electrode.
 9. A continuous inkjet printer comprising:a printhead, said printhead having a dielectric substrate and an inkdroplet deflector electrode connected to said dielectric substrate, saidink droplet deflector electrode having a first and second window, aphase detector electrode disposed within said first window and connectedto said droplet deflector electrode, and a velocity detector electrodedisposed within said second window and connected to said dropletdeflector electrode.